This invention relates to a coating composition particularly useful for producing a multiple colored, two-tone, chip resistant finish on a substrate such as an automobile or truck requiring only two curing cycles.
Transportation vehicles, such as automobile and truck bodies, are treated with multiple layers of coatings which enhance the appearance of the vehicle and also provide protection from corrosion, scratch, chipping, ultraviolet light, acid rain and other environmental conditions. Basecoat/clearcoat finishes for automobiles and trucks have been commonly used over the past two decades, in a “wet-on-wet” application, i.e., the clear coat is applied before the base coat is completely cured. In typical fashion, the basecoat/clearcoat finish is typically applied over a previously cured primer surfacer coated substrate. It is also common to apply a special chip resistant primer in the low body areas of automobile and truck bodies, during the primer surfacer application stage.
The desire for even more unique and attractive color styling has led the automobile and truck Original Equipment Manufacturers (OEM) produce vehicles with multiple colored, or “two-toned,” finishes. A typical procedure used to produce a chip resistant “two-tone” finished vehicle substrate involves the following:                I) Application of a lower body chip resistant primer over an electrocoated vehicle substrate;        II) Application of a primer surfacer to the entire substrate;        III) Bake curing the prime coated substrate;        IV) Applying a main non-accent color basecoat to the vehicle substrate;        V) Applying clearcoat over the main color basecoat;        VI) Bake curing and covering with a protective membrane, the upper body main color basecoat/clearcoat finish area of the substrate;        VII) Applying accent color in accent area        VIII) Applying accent clear in accent area        IX) Bake curing the accent basecoat/clearcoat finish, and removing the protective membrane.        
Accordingly, producing a chip resistant two-tone finished vehicle substrate typically involves three bake curing cycles and six coating stages, including passing the vehicle substrate through the basecoat/clearcoat finishing stages on two separate occasions. Several practical disadvantages arise with this typical procedure. These include two separate clearcoating steps, one additional bake curing cycle, and most notably, the requirement to pass the vehicle substrate through the basecoat/clearcoat finishing stages on two separate occasions tying up the vehicle assembly line and producing a production bottleneck. This last disadvantage is time consuming, energy demanding, and not cost effective.
Therefore, there is a need for coating compositions, which provide multiple colored two-tone finishes in a minimum number of coating layers and bake curing cycles.